This invention relates to guided missiles. More particularly, this invention relates to guided projectiles in which a guidance system provides a pathway for a warhead charge when the projectile has reached its target.
The present invention was developed for use in a guided armor-piercing artillery round. In a typical application, a strapdown gyroscope is mounted in the nose of a projectile round. The artillery round contains a warhead which includes a shaped charge which is separated from the gyroscope by electronic circuit boards. Upon detonation, the shaped charge causes material such as copper to be plastically deformed and directed past the circuit boards and gyroscope in order that the material can pierce the armor plating of a target which the projectile has struck. The circuit boards can usually accommodate the material by providing appropriate openings within the center of each circuit board. It is also possible to make circuit boards sufficiently thin that they present effectively no impediment to the flow of plastically deformed metal. The gyroscope, on the other hand, is typically mounted along the center line of the projectile's center axis. For this reason, a plastically deformed stream propelled by the shaped charge must penetrate the gyroscope. This diminishes the material's ability to penetrate armor and consequently has a detrimental effect on the shell's lethality.
Such guided shells are typically launched as 155 mm howitzer rounds. These rounds experience approximately 9,000 g's upon launch with "Zone 7" charges and up to 15,000 g's at launch with "Zone 8 super charges". Clearly, all components required to be used after launch, such as the guidance system, must be hardened to withstand the stresses imposed by the launch environment.
The gyroscope is the most difficult seeker item to harden. The gyroscope is a precision inertial measurement instrument and cannot tolerate the inducement of large drifts or biases by the cannon launch environment. A primary design problem was that the extreme launch load would damage the gimbal bearing, causing unacceptable gyroscope performance. A prior art technique was developed which added a load carrying flange to a conventional bearing design. At launch, the load transfer bearing deflected under load until a gap between the flanges closed. With the gap closed, the load carrying area is significantly increased, preventing any further deflection. With the majority of the load carried in the flange area, the bearings are protected and gyroscope performance does not change after experiencing the cannon launch environment.
These prior art load transfer bearings also had to be enhanced by the presence of a structural load carrying sleeve called a "gotcha" mechanism. The gotcha transfers the load created by the gyroscope rotor to the primary structure and prevents the load from being carried by the gimbals and bearings. The prior art gyroscope rotor only weighs 0.220 kg, but under a 9000 g launch its weight is equivalent to 1980 kg. Thus, the protection afforded by the gotcha to prevent this level from reaching the bearing was crucial. The gotcha assembly also formed an obstruction to the movement of the plastically deformed material which was intended to penetrate the armor of the target.
Accordingly, it is desirable to provide a gyroscope assembly which presents a reduced obstruction to material passing through its center. It is desired to provide a gyroscope assembly which does not require a separate gripping mechanism to protect the gyroscope during high-g launch conditions. It is further desired that the gyroscope be able to operate efficiently and accurately as soon as possible after experiencing a high-g launch in order that target acquisition and projectile guidance functions can be achieved as early as possible. It is also important to provide a gyroscope which can be used for strapdown target acquisition, which is inexpensive to produce. In furtherance of these goals, it is desirable to provide a gyroscope in which plastic components be substituted for metal components to the extent that ferromagnetic properties of the components are not required.